The present invention relates generally to multiple disc clutches which, as a major advantage over single disc clutches, have an inherent capacity for achieving greater frictional contact area per given disc diameter. This is because in multiple disc clutches the number of discs, rather than disc size, may be increased for handling greater clutch loads. More particularly the invention relates to friction clutches of the type comprising a set of driving clutch plates and a set of driven clutch discs, the plates and discs being interleaved together in alternating relationship along a common axis. Such multiple disc clutches are extensively used in heavy duty service, such as in large tractors, heavy trucks, earth moving machinery, and military tanks.
Multiple disc clutches are usually engaged by the exertion of an axial thrust against one end of the assembly or pack of clutch plates and discs. The latter thrust operates to compress the driving plates and driven discs together into firm frictional engagement. The clutch is generally released by the action of spring energy, which is arranged to allow the clutch plates and discs to separate when the aforesaid axial thrust is released.
Heretofore associated with the releasing of such clutches has been a "dragging" of some of the clutch plates with some of the friction discs, caused by failure of one or more of the clutch plates to separate from associated discs when the clutch is disengaged. This problem, when severe, has resulted in overheating of the clutch, excessive wear of the friction surfaces, and poor synchronization of associated transmission gears.
The problem is particularly acute in "wet" type clutches, which contain discs and plates contacting one another in an environment of oil. In such environments, whenever the clutch pressure plate is drawn back to disengage the clutch, the rotatable pack of interleaved discs and plates tends to adhere or stick together and be drawn away from the flywheel without separation between them. The resulting continued contact between discs and plates during idle periods of clutch disengagement generates an undesirable residual moment which in turn results in the aforementioned disadvantages.
Several attempts to provide apparatus which automatically separates the driven clutch discs from the driving clutch plates upon clutch release have resulted in equipment either less than satisfactory, or relatively expensive to manufacture. Moreover, many of such attempts have resulted in apparatus which has failed to positively restore or relocate both sets of discs and plates back into original positions, or to positively retain them in positions of idle for avoiding all frictional contact or drag between the plates and discs. Thus, an improved apparatus is needed which will positively retain both sets of discs and plates in desired positions throughout the entire idling operation of the clutch. Such a clutch would possess the attributes of improved wear of the friction surfaces, improved synchronization, and commensurately easier gear shifting.